Many different types of cooking have been performed for thousands of years by way of a variety of broadband heating sources. The earliest and most fundamental heating source widely used by man for heating was fire. It produces radiant heat energy which ranges from the UV to the long infrared. The actual shape of the output curve, which defines the strength of the radiation at each wavelength, changes as a function of the temperature of the fire. As wood and coal fires gave way to oil and gas fired ovens or cooking surfaces, the fundamentals stayed the same in that the combustion of the fire produced a broadband source of radiant energy. A knowledge base built up wrapped around the assumption of the commonly available broadband equipped oven cooking. As electricity became more commonplace in the early 20th century, electrically energized resistance based heating coils were often used instead of the various combustion-based sources. These resistance heating coils are often generically referred to in the industry as Calrods. Although they seemed new and modern to the consumer, they were still fundamentally very broadband irradiation sources. This is well known but is evidenced by the fact that a Calrod heating coil may glow bright red, which indicates output in the visible spectrum and will also produce energy continuously well out into the long infrared wavelengths. Although it is a very broadband output source, its peak output, depending on at what temperature it is operated, is typically in the long infrared category.
In the last several decades, quartz halogen lamps, tubes, and bulbs have been used in various types of oven or curing applications as well. Because the quartz approximates a much hotter blackbody Planckian source, it outputs substantially more energy in the visible spectrum than typical resistance heat sources. Different quartz lamps are designed to run at different temperatures which changes the center of its output curve, also affecting how much visible light energy it produces. The center or peak output is typically in the near infrared or middle infrared ranges. Regardless of the temperature at which they are operated, quartz is still a broadband source which has its peak output in the near to mid infrared range and with a bandwidth of several thousand nanometers.
Even tungsten filament incandescent light bulbs have been used as cooking heat sources for specialized ovens. Franklin S. Malick, in his U.S. Pat. No. 4,481,405, teaches a simple system which uses incandescent light bulbs to cook food that is in plastic cooking pouches. While quartz is a more unusual and specialized oven than simple resistance coils or burners, it is clearly broadband analog irradiation devices that are being used as the sources.
Various combinations of these modalities have been used but all of them simply combine broadband analog devices in different ways. Robert A. Mittelsteadt in his U.S. Pat. No. 4,486,639 teaches one of the earlier multimode cooking methodologies. He teaches the combination of a microwave oven with quartz lamp heating devices. By having a control option of using the quartz lamps to either directly irradiate or to heat the air and then cook by hot air convection, he combines three different functionalities into a single oven. Although microwave cooking is probably the newest fundamentally different cooking technology, the fundamental radio frequency microwaves at its heart are actually a much broader bandwidth analog source than the ones mentioned above. In fact, the only cooking devices that have been available in the marketplace prior to this invention are analog broadband types.
Ronald Lentz et al. understood and re-taught some fundamental concepts in their U.S. Pat. No. 5,382,441. They recognize that long wavelength infrared has less penetration depth with food than shorter wavelengths. They also recognize and re-taught at some depth the classic physics of Planck's law of blackbody's which describes the broadband radiation output which changes as a function of temperature of the heating device. They recognize that, while they would like to be able to control the wavelengths of output, they do not have an elegant, direct, or efficient solution to this problem. They absolutely cannot do it efficiently. They therefore teach using a broadband analog source and superimposing a filter between the radiation source and the food to be cooked. They suggest either a water filter or a treated glass filter. They recognize that even their best choice of a quartz lamp “ . . . has been determined to deliver at most 35% of its radiation between 800 and 1300 nm . . . ”. By teaching the use of a filter they are therefore going to be throwing away 65% of their energy. That 65% will be absorbed by a filter and will result in either superheating the filter and thus turning it into its own blackbody radiator, or using some external means to remove the heat from the filtration means. This is cumbersome to implement. Under either circumstance it is a highly inefficient way of eliminating the unwanted wavelengths from a broadband analog source. While they are teaching limiting the irradiation that reaches the target to approximately 500 nm of bandwidth, it still represents a broadband source. They fail to teach a high-resolution absorption curve. They therefore fail to teach or recognize that there are micro-peaks and micro-troughs in many products' absorption curves which their inefficient technique will still be incapable of addressing. For example the present invention can take advantage of the fact that; a high-resolution curve indicates pizza dough is roughly four times more absorptive at 1200 nm than it is at 900 nm. The same dough is about three times more absorptive at 1200 nm than it is at 1100 nm. Lentz fails to teach any kind of solution which would take advantage of this important data to optimize the cooking way beyond what their solution can provide. They also fail to teach a digital semi-conductor based narrowband source or how one would build or implement same. They also fail to teach what a narrowband source would bring as advantages. They also fail to teach and did not invent any “instant on”/“instant off” technology. They neither fail to teach any pulsed irradiation technology nor what the advantages would be. While they casually mentioned that their invention could be practiced with other IR radiation sources, none of them are described as digital or semiconductor-based or narrowband or directional. They further fail to teach a methodology for implementing any IR irradiation sources that accomplish direct electron to photon conversion. Clearly the thrust of their invention is comprised of using a filter to reduce or eliminate some unwanted broadband range.
Much of a fundamental concept has been generally understood for years, that the wavelength of irradiation has various effects on cooking. It is generally understood, for example, that very long wavelengths contribute to skin absorption or heating the target food very near the surface. This is why most current ovens typically are designed to not expose the food directly to the irradiation of long infrared sources unless surface heating is the desired end result. Broiler heating elements are typically mounted above the food to be cooked so that they can directly irradiate it, thus searing and cooking near the surface. Baking heating elements are, on the other hand, mounted below the food such that the pan or cooking vessel is between the food and the heating element so the food will not be directly irradiated by the longwave infrared energy. Another example of this concept is taught by David McCarter in U.S. Pat. No. 6,294,769 which is an infrared device for keeping food warm and ready to eat. Specifically, it describes a system that is useful for keeping foods, such as French fries, at a desirable temperature without resulting in substantial additional internal cooking. The concept being taught is one of using a resistive broadband ceramic heating element which produces infrared heat largely in the wavelength range from 7.91 to 4.7μ. FIG. 1 shows his absorption graph of French fries which generally shows an increasing absorption with longer wavelengths up to a peak absorption at about 5.4μ and then a sloped off absorption to the maximum wavelength shown on the graph at 7μ. The specific absorption coefficient for French fries varies from about 62% at 4.7μ to about 95% at 5.4μ and then backs down to about 73% at 7μ. What McCarter fails to teach is the use of narrowband energy and a digital source which would facilitate a precise matching of the irradiation wavelength to the exact absorption coefficient that was desired for the application. In the broadband arrangement that McCarter describes, the French fries exhibited 50% more absorption at one wavelength compared to a wavelength only 700 nm away. By using the narrowest source that he was able to find, he was not able to tune in to the absorption that would have been ideal. It is not possible with broadband sources. He also fails to teach a digital heating system which can be turned off and on instantly to maintain the food at the exact right temperature but with substantial energy savings by having a reduced duty cycle, since energy is only being consumed when the heating devices are turned on. He shows a very low resolution graph which was adequate for his purpose. However, because it lacks the resolution which would have provided the detailed absorption curve shapes, he can not and does not teach that it may be possible to get the same average absorption at a much shorter wavelength if it were possible to irradiate with a narrowband system which irradiates into a localized, micro-peak rather than a global peak.
Yang Kyeong Kim et al. taught in U.S. Pat. No. 6,348,676 a methodology for using quartz lamps for cooking. They teach, as was mentioned earlier, that the shape of the output curve can be varied as a function of what temperature the lamp is designed to function at. They show a quartz lamp which is designed to function as a 2400° K. device has its peak output at approximately 1.1μ. By comparison, a 2300° K. device has its peak output at approximately 1.25μ with a somewhat flatter output curve. Regardless of the wavelength of maximum output, the curves for both devices are shown to have substantial output throughout the visible range and out to 3μ or more in the mid infrared region. In FIG. 2, Kim shows the absorption spectral curves for different food items. While they are low resolution absorption curves, each curve is unique and different from all the others. What they generally have in common is substantially more transmission (less absorption) below about 1400 nm than above that wavelength. Kim tries to make the case that by using a quartz lamp with a lower color temperature, it is possible to cook the food faster because of higher output of longer wavelength infrared energy which will be in the generally higher absorption region, which is shown to be generally above about 1400 nm. What Kim et al. fail to teach is how to take advantage of the optimal cooking absorptions of the individual food items. Again, the food items have local, micro-peaks and micro-troughs in their absorption curves which are substantially different from one another. Substantial differences are evident even within less than 100 nm of wavelength. It is apparent that those small features were not meaningful to Kim and cohorts because the graph that is shown has very little resolution or detail. It is obvious by studying the broadband shape of the curves shown in FIG. 2 that it would not be possible to irradiate and take advantage of wavelength matching any of the micro-peaks or micro-troughs that may be characteristic of a certain food product. Similar to McCarter, they totally fail to teach a methodology for cooking with digital, narrowband irradiation to truly optimize the cooking opportunities and efficiencies.
Brian Farkas et al. in U.S. Pat. No. 7,307,243 teach yet other ways of incorporating a mix of broadband sources. They also recognized that longer wavelengths are generally absorbed closer to the surface of food items and conversely, that shorter wavelengths tend to have a greater penetration. They teach the use of Planckian, blackbody sources at different wattages and temperatures. They show by way of several graphs how these conventional analog broadband sources can be changed in terms of central wavelength and flatness of curve. They again show what is well known in physics, that the hotter a blackbody source is operated, the shorter the center wavelength will be. Correspondingly, as the wavelength grows shorter, the curve becomes somewhat steeper and more abrupt. It is again shown however that no matter how many different ways it is applied, it is still an analog broadband source of several thousand nanometers in width and whose steepness and curve changes proportional to applied voltage or current (wattage). They further recognize that the body and structure of the oven itself heats up over a period of time and becomes its own blackbody re-radiator. They teach and show that even when the heating elements are turned off there is still substantial radiant cooking that is being done in the oven as a result of the structural re-radiation. This teaches directly away from the current invention which has the ability to turn on and off instantly and warm-up time has virtually no effect on the quality of the cooking. Farkas continues to teach what has been known for many years but just in a differently configured oven arrangement. Farkas, like the others mentioned earlier, fails to teach any of the advantages that would be gained from the present invention that incorporates digital narrowband sources to take advantage of the micro-peaks and micro-valleys in the high-resolution absorption curves to optimize the desired heating or cooking. They also fail to teach the additional speed of cooking that is possible by using direct narrowband irradiation that is properly matched to the target and cooking duties.
Various other patents teach novel ways of controlling or turning the traditional analog broadband sources up or down or changing their distance from the cooking target. Donald Pettibone and cohorts with their U.S. Pat. No. 5,883,362 is an example of such a patent but it also fails to teach any of the advantages, techniques, and technology that the present invention does.